PRE Evaluation Report -- Pyrus calleryana 'Bradford' Plant Risk Evaluator -- PRE™ Evaluation Report Pyrus calleryana 'Bradford' -- Illinois 2017 Farm Bill PRE Project PRE Score: 17 -- Reject (high risk of invasiveness) Confidence: 74 / 100 Questions answered: 19 of 20 -- Valid (80% or more questions answered) Privacy: Public Status: Completed Evaluation Date: August 23, 2017 This PDF was created on June 20, 2018 Page 1/19 PRE Evaluation Report -- Pyrus calleryana 'Bradford' Plant Evaluated Pyrus calleryana 'Bradford' Image by David Stephens, Bugwood.org Page 2/19 PRE Evaluation Report -- Pyrus calleryana 'Bradford' Evaluation Overview A PRE™ screener conducted a literature review for this plant (Pyrus calleryana 'Bradford') in an effort to understand the invasive history, reproductive strategies, and the impact, if any, on the region's native plants and animals. This research reflects the data available at the time this evaluation was conducted. General Information Status: Completed Screener: Emily Russell Evaluation Date: August 23, 2017 Plant Information Plant: Pyrus calleryana 'Bradford' If the plant is a cultivar, how does its behavior differs from its parent's? 'Bradford' was the first selection of Pyrus calleryana to become commercially available in the United States in 1962. 'Bradford' was selected at the USDA Plant Introduction Station in Glenn Dale, Maryland. The crown is pyramidal with densely packed branches which are prone to structural problems and breakage, more so than later cultivars. 'Bradford', however, is the most fireblight-resistant cultivar. It is thornless, unlike the species, but is often grafted onto seedling rootstock in the nursery trade. It is self- incompatible but does produce fertile fruit after pollination by other cultivars. One study suggests 'Bradford' is among the top 3 parents of naturalized populations of Pyrus calleryana (Hardiman 2010). Any differences between cultivars are lost by the second generation, so this evaluation will use traits of the species, naturalized populations, and the horticultural cultivar as appropriate. Regional Information Region Name: Illinois Page 3/19 PRE Evaluation Report -- Pyrus calleryana 'Bradford' Climate Matching Map To answer four of the PRE questions for a regional evaluation, a climate map with three climate data layers (Precipitation, UN EcoZones, and Plant Hardiness) is needed. These maps were built using a toolkit created in collaboration with GreenInfo Network, USDA, PlantRight, California-Invasive Plant Council, and The Information Center for the Environment at UC Davis. Click here to see the generated climate matching map for this region. This climate match database is hosted by GreenInfo Network and publicly accessible. Page 4/19 PRE Evaluation Report -- Pyrus calleryana 'Bradford' Evaluation Questions These questions are based in an original article published at the University of California, Davis, and can be found on the PLOS One website, here: https://doi.org/10.1371/journal.pone.0121053 Invasive History and Climate Matching (Questions 1 - 6) 1. Has the species (or cultivar or variety, if applicable; applies to subsequent "species" questions) become naturalized where it is not native? Answer: Yes, which contributes 1 points to the total PRE score. The screener has a Very High confidence in this answer based on the available literature. Answer / Justification: The cultivar 'Bradford' is not capable of reproducing on its own due to self-incompatibility. It is however capable of crossing with other cultivars to produce offspring, and these offspring have naturalized across the eastern United States. Pyrus calleryana has also naturalized in Australia. Reference(s): Hardiman, N. A., & Culley T. M. (2010). Reproductive success of cultivated Pyrus calleryana (Rosaceae) and establishment ability of invasive, hybrid progeny. American Journal of Botany. 97, 1698–1706. USDA NRCS (2017). USDA PLANTS Database: Pyrus calleryana (Callery pear). Swearingen, J., Slattery B., Reshetiloff K., & Zwicker S. (2010). Plant Invaders of Mid-Atlantic Natural Areas. 168. 2. Is the species (or cultivar or variety) noted as being naturalized in the US or world in a similar climate? Answer: Yes, which contributes 2 points to the total PRE score. The screener has a Very High confidence in this answer based on the available literature. Page 5/19 PRE Evaluation Report -- Pyrus calleryana 'Bradford' Answer / Justification: The cultivar 'Bradford' is not capable of reproducing on its own due to self-incompatibility. It is however capable of crossing with other cultivars to produce offspring, and these offspring have naturalized across the Eastern United States, including Illinois. In an Ohio study, 'Bradford' was among the top three most common parents of naturalized plants sampled (Hardiman 2010). Reference(s): Hardiman, N. A., & Culley T. M. (2010). Reproductive success of cultivated Pyrus calleryana (Rosaceae) and establishment ability of invasive, hybrid progeny. American Journal of Botany. 97, 1698–1706. USDA NRCS (2017). USDA PLANTS Database: Pyrus calleryana (Callery pear). 3. Is the species (or cultivar or variety) noted as being invasive in the U.S. or world? Answer: Yes, which contributes 2 points to the total PRE score. The screener has a Very High confidence in this answer based on the available literature. Answer / Justification: Pyrus calleryana is listed as invasive in at least 26 states in the US. Individual cultivars themselves are not invasive, but the combination of cultivars within an area can create a situation in which invasive plants are produced. Reference(s): Hardiman, N. A., & Culley T. M. (2010). Reproductive success of cultivated Pyrus calleryana (Rosaceae) and establishment ability of invasive, hybrid progeny. American Journal of Botany. 97, 1698–1706. Mid-Atlantic Exotic Pest Plant Council (2005). Mid-Atlantic Exotic Pest Plant Council Plant List. Midwest Invasive Plant Network (2015). Midwest Invasive Plant List. Page 6/19 PRE Evaluation Report -- Pyrus calleryana 'Bradford' 4. Is the species (or cultivar or variety) noted as being invasive in the US or world in a similar climate? Answer: Yes, which contributes 3 points to the total PRE score. The screener has a Very High confidence in this answer based on the available literature. Answer / Justification: Pyrus calleryana is listed as invasive in Illinois, Indiana, Ohio, Missouri, and Maryland. Individual cultivars themselves are not invasive, but the combination of cultivars within an area can create a situation in which invasive plants are produced. Reference(s): Mid-Atlantic Exotic Pest Plant Council (2005). Mid-Atlantic Exotic Pest Plant Council Plant List. Midwest Invasive Plant Network (2015). Midwest Invasive Plant List. 5. Are other species of the same genus (or closely related genera) invasive in a similar climate? Answer: No, which contributes 0 points to the total PRE score. The screener has a Medium confidence in this answer based on the available literature. Answer / Justification: Pyrus communis and Pyrus betulifolia are listed in the Invasive Plant Atlas of the US, but neither appear to be significant invasive species in a climate similar to Illinois. Reference(s): Swearingen, J., & Bargeron C. (0). common pear: Pyrus communis (Rosales: Rosaceae): Invasive Plant Atlas of the United States. Page 7/19 PRE Evaluation Report -- Pyrus calleryana 'Bradford' 6. Is the species (or cultivar or variety) found predominately in a climate matching the region of concern? Answer: No, which contributes 0 points to the total PRE score. The screener has a Medium confidence in this answer based on the available literature. Answer / Justification: Pyrus calleryana distribution in the southern and western United States, Africa, Australia, and southern China are not a climate match with Illinois. Reference(s): GBIF (0). Pyrus calleryana Decne. - gbif. Impact on Native Plants and Animals (Questions 7 - 10) 7. Does this plant displace native plants and dominate (overtop or smother) the plant community in areas where it has established? Answer: Yes, which contributes 1 points to the total PRE score. The screener has a Very High confidence in this answer based on the available literature. Answer / Justification: "Because of its rapid growth and preference for high light environments, P. calleryana can potentially impede the establishment of late- to middle-stage successional species in disturbed sites." "Once established Callery pear forms dense thickets that push out other plants including native species that can’t tolerate the deep shade or compete with pear for water, soil and space. A single tree can spread rapidly by seed and vegetative means forming a sizeable patch within several years. Its success as an invader results from its capacity to produce copious amounts of seed that are dispersed by birds and possibly small mammals, seedlings that germinate and grow rapidly in disturbed areas and a general lack of natural controls like insects and diseases, with the exception of fire blight." Page 8/19 PRE Evaluation Report -- Pyrus calleryana 'Bradford' Reference(s): Culley, T. M., & Hardiman N. A. (2007). The Beginning of a New Invasive Plant: A History of the Ornamental Callery Pear in the United States. Bioscience. 57, 956–964. Texas Invasives (0). Texas Invasives - Pyrus calleryana. 8. Is the plant noted as promoting fire and/or changing fire regimes? Answer: No, which contributes 0 points to the total PRE score. The screener has a Medium confidence in this answer based on the available literature.